Methods for producing nonadherent avian cell lines

ABSTRACT

The present invention relates to a method for producing avian cell lines, comprising gradual or complete withdrawal of growth factors, serum and/or feeder layer so that the established lines are adherent or nonadherent cells capable of proliferating indefinitely in a basic culture medium. The invention also relates to the cells derived from such lines which are particularly useful for the production of substances of interest.

The present invention relates to a method for producing avian celllines, in particular avian stem cells, comprising progressive or totalwithdrawal of growth factors; serum and/or feeder layer. Thesespontaneously established lines are adherent or nonadherent cellscapable of proliferating indefinitely in a basic culture medium. Theinvention also relates to the cells derived from such lines which areparticularly useful for the production of vaccines and of substances ofinterest.

Stem cells are cells identified by their culture in vitro from anembryo, from part of an embryo or even from an adult tissue. Theexpression stem cell is understood to mean any pluripotent cell ofembryonic or adult origin which has a capacity for self-renewal and iscapable of giving specialized differentiated cells. In other words, anynoncancerous cell capable of dividing indefinitely in culture and ofgiving a daughter cell having the same capacity for proliferation anddifferentiation as the mother cell from which it is derived. Theseisolated cells exhibit particular morphological and immunocytochemicalcharacteristics. It is also possible to distinguish the notion of:

-   -   embryonic stem cells (CES cells), stem cells which have the        characteristic feature of being obtained from culturing parts or        all of a very early embryo (blastula stage). These CES cells        exhibit in vitro all the characteristics of a stem cell, and in        vivo the unique capacity of contributing to the morphogenesis of        an embryo and of participating in germline colonization when        they are reimplanted in any manner whatsoever in a recipient        embryo.    -   somatic stem cells (SSC), cells which have all the        characteristics of stem cells when they are cultured in vitro,        but which, unlike CES cells, do not have the potential to        colonize in vivo the gonads after infection into an embryo. They        contribute solely to the morphogenesis of the somatic tissues in        the embryo.

Unlike already differentiated primary cells, stem cells do not exhibitan easily identifiable characteristic state of morphologicaldifferentiation (fibroblasts, adipocytes, macrophage, and the like), butare rather characterized by a state of proliferation and ofnondifferentiation. This state results in different behaviors such as arapid proliferation in vitro, a characteristic morphology, the presenceof different markers, variable requirements for growth factors and anability to respond to particular stimuli for induction ofdifferentiation. They are not sensitive to replicative senescence, acritical period for a large number of differentiated primary cells,including the fibroblasts for example.

To maintain avian stem cells in vitro for long periods of time, it isnecessary to observe specific culture and maintenance conditions asdescribed in Pain et al., 1996; U.S. Pat. No. 6,114,168 and EP 787 180.

The in vitro culture of a primary cell under satisfactory medium andgrowth factor conditions allows it to proliferate only for a certainnumber of passages. This cell can be obtained directly from adissociated tissue or from part of this tissue. This number of passagesis nevertheless highly dependent on the animal species considered, onthe origin of the tissue, on the age of the donor organism and the like.

In most cases, the cell proliferation observed in vitro slowsprogressively and then the cells stop proliferating.

This arrest often corresponds to a replicative senescence, known by theterm Hayflick limit. This stoppage is thought to be the result of theaction of a true molecular clock of which one of the key components isthought to be the length of the telomeres. The telomeres are repeatsequences situated at the end of the chromosomes. The shortening ofthese repetitive nucleotide structures is the consequence of thereplication of DNA on a semiconservative mode. In the absence of thetelomerase enzyme, which is in charge of adding the repeat sequences atthe end of the chromosomes, a point of no-return is reached with regardto the size of the telomeres, a point beyond which an as yet unknownmolecular mechanism for activation of genes involved in controlling thecell cycle is triggered. The cells are then thought to be blocked in theG1 phase in their divisions and are thought to stop proliferating.Numerous factors appear to be involved in this negative control of thecell cycle such as various cyclins, specific kinases, RB and P53proteins, specific transcription factors such as E2F and many others(mdm2, BTG, p21, and the like). Conversely, the telomerase enzyme cantherefore be viewed as a central factor in cell immortality because itmaintains the length of the telomeres and therefore makes the cellinsensitive to this loss caused by successive divisions.

In an organism under development and during the life of this organism,only a few cell types, including certain lymphocytes, exhibit apermanent expression of telomerase. This activity also appears to be oneof the characteristics of stem cells, both at the somatic level (SSC)and at the germline level. This property of expressing, of maintainingof expression and of “awakening” expression of the telomerase activityis also often associated with the immortal character of a cellmaintained in vitro. To date, numerous cancer cells are also detectedpositive for telomerase activity. This activity is thought to bepartially responsible for the capacity for uncontrolled proliferation oftumor cells in vivo.

This telomerase activity is, in all cases, an excellent marker for thestem cell character and for the germline lineage and for the capacity ofa cell to become immortal. Two criteria are therefore used: thetelomerase activity and the size of the telomeres.

In an establishment perspective and very briefly, according to theliterature and the results already available in many laboratories, theestablishment of cell lines may be carried out according to two routes:a spontaneous establishment resulting from noninduced intrinsic geneticdamage or a triggered establishment, induced by the use of viruses,retroviruses or by other means such as chemical agents, irradiation, UV(ultraviolet) radiation, and the like. In mammals, for example, theestablishment of rodent (mouse, rat, and the like) cells is recognizedas being fairly easy spontaneously; on the other hand, the situation isquite different for human cells regardless of their tissue origin (Smithand Pereira-Smith, 1996).

Thus, when it is desired to obtain cell lines from the abovementionedavian stem cells so as to produce a mass of substances of interest invitro, the problem is to be able to maintain cells in culture in aneconomical medium while avoiding stumbling blocks such as cellulardifferentiation and senescence.

At the avian level, it is generally accepted that the establishment ofprimary cells is a rare, or even practically nonexistent event. The onlynotable published exception appears to be the DF-1 line which resultsfrom the immortalization, described as being spontaneous, of chickenfibroblasts (Foster et al., 1991; U.S. Pat. No. 5,672,485, ATCC No. CRL12203). At the level of this line, recent articles mention the firstcomponents of observed deregulation (Kim et al., 2001a; Kim et al.,2001b).

In the immortalization process, a first step leads the proliferatingcell to the Hayflick limit which, depending on the cell types, isbetween 10 and 50 passages. A first spontaneous mutational event thentakes place which allows the cell to cross this first blockage, an eventwhich often affects the p53 and pRb genes, and the like. The cellstherefore continue to proliferate until the moment when a secondblockage occurs, which is in general lifted by new mutations in othergenes and by the activation of telomerase, which is often observed.

At the avian level, it is in general accepted that the establishment ofimmortal primary cells is a practically nonexistent event. Accordingly,a large number of lines have been obtained by culturing tumor cells,often directly taken from a biopsy of the tumor.

This obtaining in vitro is in fact the result of the impairment in vivoof certain genes, which are responsible for the appearance of the tumor.An example is provided by the fibroblast line SB-CEV-1, which isisolated from the culturing of a visceral tumor from an animal (ATCC No.CRL 10497, U.S. Pat. No. 5,846,527). This approach is greatlyfacilitated by the existence of a very large number of avian viruses andretroviruses which have been identified, isolated and oftencharacterized at the molecular level. Being often oncogenic by theirdirect or indirect action (activation of a transforming endogenous geneduring their integration, expression of the oncogenic protein(s)endogenous to the virus), these viruses cause tumors and lesions; thus,the obtaining of cell lines in different differentiated lineages ispossible from the culturing of the infected organs of the animals. Thein vitro use of these viruses, and retroviruses, isolated in vivo, hasbeen developed in addition. There may thus be mentioned nonexhaustively:

-   -   the lymphoblastoid lines DT40 and DT95, obtained in the presence        of the avian leukosis virus (ALV) and in which the myc locus is        activated (Baba et al., 1985, ATCC No. CRL 2111, CRL 2112),    -   the turkey lymphoblastoid line MDTC-RP19, established with the        Marek's disease virus (U.S. Pat. No. 4,388,298, ATCC, No. 8135),    -   the lymphoblastoid line ConA-C1, established with the REV virus        (reticuloendothelial virus, ATCC No. 12135, U.S. Pat. No.        5,691,200),    -   the myelomonocytic line BM2 established with the MH2 virus (Liu        et al., 1977, U.S. Pat. No. 5,388,680),    -   and a whole series of hematopoietic lines obtained with        different viruses,        -   the erythroblastic line HD4 (6C2), obtained with the AEV            virus        -   the monocytic line HD11 (Beug et al., 1979), obtained with            the MC29 virus        -   the granulocytic line HD13 (Golay et al., 1988), obtained            with the E26 virus        -   the mixed hematopoietic line IID57 (Metz and Graf, 1991)            also obtained with the E26 virus.

However, the problem in these transformation approaches is the obtainingof cells which produce viruses and carry the activated genome of theviruses and retroviruses used. These activations and this viral presenceare brakes on their industrial use as replication support for viruses ofinterest or for the production of specific proteins under optimum safetyconditions.

Another approach to overexpression of oncogenes, of immortalizing genes(adenovirus E1A gene, polyoma SV40 “large T”, and the like) or genefragments has also made it possible to obtain lines from alreadydifferentiated primary cells. These components may be introduced intothe cells by simple transfection of a vector allowing the expression ofthe immortalizing part, but may also be introduced via viruses orretroviruses which have been genetically modified to express theseimmortalizing components. The origin of the immortalizing components maybe avian or otherwise, viral or otherwise. The tropism for avian cellscan in fact be linked to the original virus or can also be modified. Byway of example, the duck fibroblast line TDF-2A is thus obtained byintroducing a first immortalizing gene and then an antiapoptotic gene(Guilhot et al., 1993, U.S. Pat. No. 6,255,108). Other methods have beendeveloped, such as the overexpression of p53 (Foster et al., U.S. Pat.No. 5,830,723).

In addition, the action of chemical carcinogens directly on the animalaccording to different modes of administration has allowed, inter alia,the obtaining

-   -   of the QT6 and QT35 lines, of quail fibroblasts (Moscovici et        al., 1977, ATCC No. CRL 1708),    -   of the chicken hepatocyte line LMH (Kawaguchi et al., 1989, ATTC        No. CRL 2117),    -   of the chicken fibroblast line CHCC-OU2 (ATCC No. CRL 12302,        U.S. Pat. No. 5,989,805).

The expression immortalization event is understood to mean variousactions such as:

-   -   the action of oxidative, heat or chemical stress capable of        inducing modifications in the physiology of the cells and/or        mutations,    -   the action of the products of specific genes in the physiology        of the cells, such as certain immortalizing genes (oncogenes,        protooncogenes, cell cycle genes, antiapoptotic genes and the        like),    -   targeted destruction by functional recombination or inactivation        of antioncogenes, apoptotic genes, tumor suppressor genes,        antiproliferative genes, leading to a functional deregulation of        the cell cycle or of the physiology of the cell,    -   the control of proliferation genes by their functional blocking,        and the like,    -   the action of rays (UV, gamma, X, and the like),    -   the action of chemical mutagens (substances which damage DNA,        substances similar to growth factors, and the like),    -   the conjugated action of these various actions taken separately.

In the context of the invention, it has been found that the withdrawalof growth factors, serum and/or feeder layer leads to the isolation ofpopulations of stem cells, in particular of somatic stem cells, whichcan grow indefinitely in basic culture media.

In addition, apart from the hematopoietic stem cells which are for themost part nonadherent cells, the majority of the cells, obtainedaccording to the prior art techniques mentioned above (fibroblasts,hepatocytes, and the like), exhibit an adherent phenotype. Now, theindustrial use of cells, as viral replication support, favorsnonadherent cells. This phenotype is advantageous both because of easeof handling which avoids the use of a proteolytic enzyme fordissociation and for the high densities reached by nonadherent cellscultured in vitro.

The present invention describes the production of lines which can becomespontaneously nonadherent and for which the nonadherence is obtained bya withdrawal of the feeder layer. Because of their growth in suspension,these lines are perfectly suitable for industrial use for the productionof substances of interest in bioreactors.

In addition to their properties of growing on a basic culture medium, ithas been discovered that these cell lines allow the replication ofcertain viruses in yields equivalent to or even higher than the yieldsobtained with current methods, which makes these cells particularlyuseful for the mass production of vaccines.

DESCRIPTION

Thus, in a first aspect, the present invention relates to a method forproducing avian cell lines, characterized in that it comprises thefollowing steps:

a) culturing avian cells in a medium containing all the factors allowingtheir growth and an inactivated feeder layer,b) passage by modifying the culture medium so as to obtain progressiveor total withdrawal of said factors, of the serum and/or of the feederlayer,c) establishing adherent or nonadherent cell lines capable ofproliferating in a basal medium in the absence of exogenous growthfactors, serum and/or inactivated feeder layer.

In the context of the invention, the expression “establishment of aline” is understood to mean maintaining cells in culture in vitro over aconsiderable period of time. Advantageously, the cells derived from thelines obtained in step c) are capable of proliferating for at least 50days, 100 days, 150 days, 300 days or preferably at least 600 days. The600 days do not constitute a time limit because the cell lines obtainedare still alive after much longer time periods. Hence, these lines areconsidered as being able to grow indefinitely in a basic culture mediumfree of exogenous growth factors, serum and/or inactivated feeder layer.The expression “line” is understood to mean any population of cellscapable of proliferating indefinitely in culture in vitro whileretaining to a greater or lesser degree the same morphological andphenotypic characteristics.

The cells derived from the lines according to the invention may be avianstem cells, in particular avian somatic stem cells.

The stem cells according to the invention can serve to obtaindifferentiated cell lines. Indeed, these stem cells have the property ofbeing pluripotent, that is to say that they have the potential to beinduced in multiple differentiation pathways which can be characterizedby various specific markers.

These cells can also be precursor cells, which correspond to thepartially differentiated cells of an adult or embryonic tissue, bycontrast to a stem cell and which is capable of dividing and of givingmore differentiated cells. The expression “differentiated cell” isunderstood to mean any specialized cell of an adult or embryonic tissue,having specific markers or fulfilling specific physiological functions.It is possible, in a particular aspect of the invention, in particularfor particular isolates or clones derived from a particular isolateobtained during establishment, for these stem cells to contribute to thegermline. In this case, these stem cells established as lines arethought to be embryonic stem cells.

Of course, the method mentioned above makes it possible to obtaincellular clones derived from cells obtained from established lines.These clones are cells which are genetically identical to the cell fromwhich they are derived by division.

In a particular embodiment, the invention relates to a method as definedabove, in which the established lines are adherent stem cells whichproliferate in the absence of inactivated feeder layer.

In this regard, in the method described above, step b) consists in awithdrawal of the components of the medium (growth factors alone orserum alone or growth factors and then serum or alternatively serum andthen growth factors). We also found that it is possible to obtain nonadherent cells after several passages, at any moment, from theseadherent stem cells that proliferate with or without feeder layer.

In another embodiment, the invention relates to a method as definedabove in which the established lines are nonadherent stem cells whichproliferate in suspension in a medium free of exogenous growth factors.

In this regard, in the method described above, step b) consists in aprogressive or total withdrawal of the feeder layer and then optionallyin a withdrawal of the other components of the medium (growth factorsand serum).

In another embodiment, the invention relates to a method as describedabove in which the established lines are nonadherent stem cells whichproliferate in suspension in a medium free of serum (serum-free medium).

In another embodiment, the invention relates to a method as definedabove, in which the established lines are nonadherent stem cells whichproliferate in suspension in a medium free of exogenous growth factorsand serum.

In another alternative, step b) consists in progressive or totalwithdrawal of the growth factors, optionally followed by a progressivewithdrawal of the serum.

In another alternative, step b) consists in a progressive or totalwithdrawal of the growth factors and/or serum, optionally followed by awithdrawal of the feeder layer.

In addition, the established lines may be cells which proliferate in aserum-depleted medium, in particular in a medium free of serum. Theexpression serum-depleted is understood to mean a gradual reduction ofthe concentration of serum spread out over time. This method allows aselection of clones which adapt to these new, increasingly drasticconditions until stable lines are obtained which are capable of growingin a serum-depleted medium or in a medium completely free of serum.

The method described above may additionally comprise a step in which thecells obtained in step c) are subjected to a selection in culture mediaused for large-scale production so as to obtain clones suitable for theproduction of vaccines intended for human or animal therapy.

The cells according to the invention have at least one of the followingcharacteristics:

-   -   a high nucleocytoplasmic ratio,    -   an endogenous alkaline phosphatase activity,    -   an endogenous telomerase activity,    -   a reactivity with specific antibodies selected from the group of        antibodies SSEA-1 (TEC01), SSEA-3, and EMA-1.

Preferably, the cells of the invention have all the abovementionedcharacteristics.

In an additional aspect, the invention relates to a method for producingavian lines, which is mentioned above, in which the cells derived fromthe lines obtained in step c) are modified in order to allow a betteruse in vitro such as the extension of the greater life span or growthdensities or alternatively of the lower nutrient requirements.

Advantageously, the cells derived from established lines are modified inorder to produce a substance of interest, in particular a polypeptide ofinterest, an antibody or an attenuated virus. Said cells may be modifiedby any technique accessible to persons skilled in the art, in particularhomologous, directed and/or conditional recombination (Cre-Lox orFLP-FRT system), by transformation with any vector, plasmid, inparticular with the aid of retroviruses.

The medium used in step a) may comprise at least one factor selectedfrom cytokines, in particular LIF, IL-11, IL-6, IL-6R, CNTF, Oncostatinand other factors such as SCF, IGF-1 and bFGF.

In addition, the inactivated feeder layer used in step a) is preferablycomposed of fibroblasts, including mouse fibroblasts established as aline. Among these fibroblasts are in particular the STO cells which mayor may not be modified or transfected with expression vectors (Pain etal., 1996). In this method, the cells used in step a) are cells obtainedby suspending cells obtained from blastodermal disks of fertilized eggsin a culture medium comprising at least one cytokine, b-FGF, and SCF.Said cells are inoculated into a layer of feeder cells, incubated, andthen collected.

Step b) consists in a progressive withdrawal of each growth factor addedto the medium in step a), in particular a cytokine, b-FGF, and SCF,comprising a passage in a new medium free of at least one of saidfactors and in repeating various successive passages until the medium isfree of all of said factors. The expression progressive withdrawal isunderstood to mean a removal factor by factor from the culture medium.Alternatively, it is possible to carry out a drastic or totalwithdrawal, that is to say the removal of all of said factors all atonce. Thus, the withdrawal of step b) may consist in progressivelyreducing the concentration of one or more factors or in culturing theavian stem cells directly in a medium free of one or more factors oralternatively free of all of said factors.

Step b) may also comprise the withdrawal of the serum. In this regard,the withdrawal may be progressive, by reducing the serum concentrationduring each passage, for example on passing from 10% to 7.5% and then3.75% and 2%, tending toward 0% (serum-free medium). Alternatively, adrastic withdrawal may be carried out.

Step b) may also comprise the withdrawal of the feeder layer. Thewithdrawal of the feeder layer may also be gradual, by reducing thenumber of inactivated feeder cells during each passage. Alternatively,it is possible to carry out a drastic withdrawal.

Of course, the order of withdrawals can vary. For example, it ispossible to start with the withdrawal of the growth factors and continuewith the withdrawal of the feeder layer.

Thus, in another aspect, the invention relates to the established celllines and to the cells derived from said lines which can be obtainedfrom the method described above, said cells being capable ofproliferating for at least 50 days, 100 days, 150 days, 300 days, orpreferably at least 600 days in a medium free of exogenous growthfactor, serum and/or feeder layer.

These cell lines and the cells derived therefrom are capable ofproliferating for at least 50 days, 100 days, 150 days, 300 days, orpreferably at least 600 days in a basal medium, in particular in amedium such as DMEM, GMEM, HamF12 or McCoy supplemented with variousadditives commonly used by persons skilled in the art. Among theadditives, there may be mentioned nonessential amino acids, vitamins andsodium pyruvate.

The invention also relates to the cell lines and the cells derived fromsuch lines described above, characterized in that they are avian stemcells, in particular avian somatic stem cells or avian embryonic stemcells.

These stem cells may be adherent, while proliferating in the absence ofthe inactivated feeder layer. Alternatively, these stem cells arenonadherent and proliferate in suspension in a basal medium mentionedabove.

These cells are also characterized in that they have at least one of thefollowing characteristics:

-   -   a high nucleocytoplasmic ratio,    -   an endogenous alkaline phosphatase activity,    -   an endogenous telomerase activity,    -   a reactivity with specific antibodies selected from the group of        antibodies SSEA-1 (TEC01), SSEA-3, and EMA-1.

Advantageously, these cells are genetically modified so as to produce asubstance of interest, in particular a polypeptide of interest, anantibody or an attenuated virus.

Cells of the invention can for example support the replication of liveor attenuated viruses, in particular the viruses selected from the groupof adenoviruses, hepadnaviruses, herpesviruses, orthomyxoviruses,papovaviruses, paramyxoviruses, picornaviruses, poxviruses, reovirusesand retroviruses.

Preferably, the viruses belong to the family of orthomyxoviruses, inparticular the influenza virus, to the family of paramyxoviruses, inparticular the measles, mumps and rubella viruses.

In another embodiment, the viruses replicated on these cells belong tothe to the family of poxvirus, in particular canarypox virus, fowlpoxvirus as well as vaccinia virus.

Thus, the invention relates to the cell lines described above, the cellsderived from said lines and also the cell lines obtained from cellswhich have been genetically modified. Preferably, the invention relatesto the cell lines derived from step c) of the method described above,characterized in that they are avian stem cells capable of growingindefinitely in a basal medium free of exogenous growth factors,depleted of serum or free of serum and/or of feeder layer.

In another aspect of the invention, the cells obtained at the end ofstep c) may be genetically modified.

The invention also relates to a cell culture comprising cells derivedfrom the cell lines described above, in particular avian stem cells oravian embryonic stem cells, and a basal medium free of exogenous growthfactors depleted of serum or free of serum and/or of inactivated feederlayer.

In an additional aspect, the invention relates to the use of the celllines and cells described above for the production of substances ofinterest, in particular of proteins of therapeutic interest, for thereplication of live or attenuated viruses, in particular viruses chosenfrom the group of adenoviruses, hepadnaviruses, herpesviruses,orthomyxoviruses, papovaviruses, paramyxoviruses, picornaviruses,poxviruses, reoviruses and retroviruses.

Preferably, the cell lines and the cells described above are used forthe production of viruses belonging to the family of orthomyxoviruses,in particular the influenza virus, and for the production of virusesbelonging to the family of paramyxoviruses, in particular the measles,mumps and rubella viruses.

It is possible to introduce into these lines and cells, used forsupporting the replication of live or attenuated viruses, thecomponent(s) necessary for accomplishing the complete viral cycle of thevirus so as to obtain, for example, the overexpression of the receptorfor the virus at the surface of the cell.

Therefore, one best mode of the invention is to use the cells as definedabove to produce live or attenuated vaccine, for example recombinantvaccine, comprises culturing the adherent or non adherent cell linesestablished in step c) according to the process described above,inoculating said cells with viral particles and culturing said cells ina basal medium as mentioned above until cell lysis occurs and newlyproduced viral particles are released in said medium. The invention hasshown to be particularly useful for the production of attenuated virusbelonging to the family of poxvirus, in particular canarypoxvirus,fowlpoxvirus and vaccinia virus such as such as native or recombinantvaccinia virus (for example Modified Vaccinia virus Ankara, MVA (such asMVA available under ATCC Number VR-1508) or other orthopoxviruses) andis further described in the examples below.

Furthermore, the invention is aimed at the use of the cells according tothe invention for producing recombinant viruses expressing antigens asvaccine against infection diseases such as smallpox and cancer (forexample melanoma, prostate cancer, breast cancer, lung cancer, ovarycancer, liver cancer . . . ).

For the remainder of the description, reference will be made to thelegend to the figures below.

LEGEND

FIGS. 1-3: Growth curves for the cell lines of the invention (withwithdrawal of serum (FIG. 2) and with withdrawal of feeder layer (FIG.3).

FIG. 4: Photograph, showing the characteristic morphology of avian stemcells

N: nucleus, n: nucleolus and C: cytoplasm(isolate S86N99, ×40 magnification, photograph taken with a SonyCyber-shot digital camera)

FIG. 5: Photograph showing the alkaline phosphatase activity of avianstem cell lines which are adherent or which are in suspension

After fixing (0.1% formaldehyde/0.5% glutaraldehyde, 30 minutes at 4°C.), the cells are rinsed twice in 1×PBS and incubated for between 10and 30 minutes at 37° C. in an NBT/BCIP (Nitro Blue Tetrazolium chloride0.375 mg/ml, 5-bromo-4-chloro-3-indolyl phosphate 0.188 mg/ml, 0.1M TrispH 9.5, 0.05M MgCl², 0.1M Nacl) solution. The reaction is stopped by two1×PBS washes and the photographs are taken.A—illustrates the characteristic violet coloration of the endogenousalkaline phosphatase activity obtained with the adherent line S86N45p87, a line cultured with no feeder or factor (×40 magnification, SonyCyber-shot digital camera).B—illustrates the violet coloration characteristic of the endogenousalkaline phosphatase activity obtained with the EB14 line maintainedfrom 8 passages in suspension, line derived from the S86N45 cells,cultured in suspension with no feeder or factor (×20 magnification, SonyCyber-shot digital camera).

EXAMPLE 1 Variable Origin of the Live Material Used

The establishment of cell lines is often greatly linked to the geneticnature of the cell material. Thus, in the murine example,proportionately few genetic bases are permissive to the production ofembryonic stem ES cells and often involves a notion of inbred animals.In the case of avian animals, it is difficult to obtain inbred animalsfor historical reasons and because of the origin of selection ofcommercial strains; it being of interest precisely to avoid inbreeding.Eggs are the initial source of the cells cultured in this invention. Theeggs are preferably used nonincubated, but a few hours of incubation maybe necessary in order to obtain the first stages of development of theembryo. The cells obtained are derived from different chicken strains.Among the strains used, there may be mentioned the S86N strain, acommercial strain intended for the production of chicken bearing aquality label, CNRs, the strain intended for the production of chickenbearing a quality label, Marens, a local strain which is genetically andphenotypically well characterized, White Leghorns, a strain moreintended for the production of eggs for consumption and a referencestrain for research laboratories, and the like. In the latter strain,various origins have been tested including certain eggs (called Valo)obtained from the White Leghorn strain from Lohmann (Germany) consideredto be “SPF” (Specific Pathogen Free) eggs kept under very particularhealth safety conditions. Numerous cell isolates were obtained fromvarious strains, suggesting the general character of the method.

EXAMPLE 2 Production and Establishment of the Adherent Cells

The eggs are opened, the yolk is separated from the egg white during theopening. The embryos are removed from the yolk either directly or withthe aid of a Pasteur pipette, or with the aid of a small absorbentfilter paper (Whatmann 3M paper), cut out beforehand in the form of aperforated ring with the aid of a punch. The diameter of the perforationis about 5 mm. These small rings are sterilized using dry heat for about30 minutes in an oven. This small paper ring is deposited on the surfaceof the yolk and centered on the embryo which is thus surrounded by thepaper ring. The latter is then cut out with the aid of small pairs ofscissors and the whole removed is placed in a Petri dish, filled withPBS or with a physiological saline. The embryo thus carried away by thering is cleaned of the excess yolk in the medium and the embryonic disk,thus freed of the excess vitellin, is collected with a Pasteur pipette.

In both cases, the embryos are placed in a tube containing physiologicalmedium (1×PBS, Tris Glucose, medium, and the like). The embryos are thenmechanically dissociated and inoculated on a “feeder” into definedculture medium. Among the preferred conditions used for the culturing,preference is given to the culture medium composed of MacCoy medium asbasal medium supplemented with fetal calf serum at an initialconcentration of 12 to 8%, with nonessential amino acids at 1%, with amixture of vitamins of commercial origin at 1%, with sodium pyruvate ata final concentration of 1 mM, with beta-mercaptoethanol at a finalconcentration of 0.2 mM, glutamine at a final concentration of 2.9 mM,with an initial mixture of antibiotics containing gentamycin at a finalconcentration of 10 ng/ml, penicillin at a final concentration of 100U/ml and streptomycin at a final concentration of 100 μg/ml. Rapidlyafter the first passages of the cells, the mixture of antibiotics is nolonger added to the medium. The expression rapidly is understood to meanafter the first 3 to 5 passages in general. A mixture of nucleosides mayalso be added, this mixture being prepared as described above (Pain etal., 1996). Among the basal media tested under these same conditions andwhich give similar results are the HamF12, Glasgow MEM and DMEM media,the latter supplemented with biotin at a final concentration of 8 mg/l.By way of comparison, the biotin concentration is 0.2 mg/l in the MacCoymedium, 0.0073 mg/l in the HamF12 and 0 in the commercial DMEM and GMEMmedia.

The growth factors and the cytokines added to the culture medium arepreferably factors and cytokines which are recombinant, including mouseSCF at a final concentration of 1 ng/ml, IGF-1 at a final concentrationof 1 to 5 ng/ml, CNTF at a final concentration of 1 ng/ml, IL-6 at afinal concentration of 1 ng/ml, and the soluble IL-6 receptor at a finalconcentration of 0.5 ng/ml to 1 ng/ml. In some experiments, some otherfactors may be added during the first passages. For example up topassage 3 or 10, it is possible to add bFGF to the medium at a finalconcentration of 1 ng/ml and IL-11 at a final concentration of 1 ng/ml.

The inoculation is carried out into this medium on the inactivated“feeder” composed of mouse fibroblasts established as lines, the STOcells. In some cases, these cells were transfected with simpleexpression vectors allowing the expression of growth factors such asavian SCF, constitutively in the STO cells. Thus, this “feeder” producesthe factor in a form which is soluble and/or attached in the plasmamembrane of the cells.

After initial inoculation of the cells directly into this medium, themedium is partially changed the next day, and then partially orcompletely during subsequent days, depending on the rate of adhesionobserved for the primary cells. After about 4 to 7 days depending on thecases, the initial culture is dissociated and transferred into newdishes in the same initial medium on the inactivated feeder. After threeto five passages, the cells are cultured on an inactivated feeder of STOcells which are nontransfected or transfected with an expression vectorencoding a resistance to an antibiotic such as the gene for resistanceto neomycin, to hygromycin, to puromycin and the like. After abouttwenty passages, the cells are progressively deprived of growth factorsand cytokines. The expression gradual withdrawal is understood to mean aremoval factor by factor from the culture medium. Thus, at one passage,SCF is first of all removed, and then, two or three passages later,IGF-1. If the cells do not exhibit morphological alterations or avariation in their average rate of proliferation, the other factors,such as CNTF and IL-6, are then removed. This withdrawal may also bedrastic. All the factors are in this case removed all at once. The cellsare then observed and are only passaged several days later if their rateof proliferation is modified. The latter solution is generally thatwhich is practiced.

Various isolates are thus obtained and maintained for very long periodsof time. The expression very long periods of time is understood to meanperiods of the order of several weeks with a minimum of 50 days,preferably periods greater than 200 to 400 days, without limitation intime. Periods greater than 600 days are observed.

Regardless of the support used, all the cells which are adherent aredissociated with a proteolytic dissociation enzyme, such as pronase,collagenase, dispase, trypsin, and the like. Preferably, a proteolyticenzyme of bacterial origin is used in order to avoid any potentialcontaminant of animal origin.

These cells have the characteristics of embryonic stem cells with aspecific morphology illustrated, by way of example, by the photograph ofFIG. 4 i.e. a small size, a large nucleocytoplasmic ratio, a nucleuswith at least one nucleolus which is clearly visible and a very smallcytoplasm. These cells are characterized by growth in the form of moreor less compact solid masses. The adherent and nonadherent cells exhibitcross-reactivity with a number of antibodies, as described above in Painet al., 1996 and in patents U.S. Pat. No. 6,114,168 and EP 787 180. Theendogenous telomerase activity component is also present and is animportant factor in the “stem” nature of these cells.

Cells of different isolates are obtained and maintained for long periodsof time.

Table 1 illustrates a few of the characteristics of these isolates

Gener- Name Species Start “Stoppage” Days Passage ation S86N16 Chicken26-01-2000 05-08-2001 559 207 692 S86N WL3 Chicken 28-06-2000 09-08-2001403 153 333 WL Valo4 Chicken 26-09-2000 07-02-2002 401 135 317 ValoS86N45 Chicken 29-01-2001 12-11-2001 287 118 329 S86N

It will be noted that the term “stoppage” does not correspond to the endof the proliferation of the cells but to a deliberate stoppage of thecell cultures by the experimenter. The number of generation n isobtained by the formula X=2^(n) or X is the theoretical cumulativenumber of cells. This number is available since the cells are counted ateach passage and during each inoculation. The complete history of theculture is thus available.

EXAMPLE 3 Passage of the Cells

One of the characteristics of stem cells, in particular somatic stemcells and embryonic stem cells, is their capacity to proliferate invitro for considerable periods of time. In order to propagate and topassage the cells, the culture medium is changed and replaced with freshmedium a few hours before their passage The curve presented in FIG. 1illustrates a profile of cell growth and establishment.

EXAMPLE 4 Doubling Time and Average Division Time

Starting with the established cells in culture and the cells presentedin the preceding examples, a mean division time can be calculated. Forall the independent isolates obtained, the rate of proliferationincreases slightly during successive passages, thus causing the averagedivision time during the establishment of the cells to vary. In theadherent phase, the cells are initially inoculated on an inactivatedfeeder layer and are passaged regularly at a constant initialinoculation density of 1 to 2×10⁶ cells per 100 mm dish. Table 2illustrates the doubling time (d) and the mean division time (MDT inhour) for 3 established cell types as a function of the culture time. Itis observed that the mean doubling time decreases during theestablishment.

TABLE 2 Cells/days 50 100 150 200 250 300 350 400 450 500 550 S86N16 (d)0.30 0.63 1.00 0.86 1.13 1.15 1.47 1.70 1.94 1.50  1.9 S86N16 (MDT) 8038 24 27.9 21.2 20.9 16.3 14.1 12.4 16 12.6 S86N45 (d) 0.49 0.89 0.891.45 2.15 x x x x x x S86N45 (MDT) 49 26.8 27 16.5 11.1 x x x x x xValo4 (d) 0.03 0.61 1.00 1.17 1.26 1.03* 1.08* 1.25* x x x Valo4(MDT) >48 39.3 24 20.5 19 23.3 22.2 19.2 x x x

The mean doubling time d is established for the period of time indicatedin days with the following formula: d=(1/Log 2×(Log X2/X1))×1/(T2−T1)where X2 and X1 are total numbers of cells at the times T2 and T1. Thisformula is the direct consequence of the calculation of the number ofgenerations N by the formula X=2^(n) presented in example 1. The meandivision time (MDT) is then obtained in hours by dividing 24 hours by d.

* The Valo cells are passaged during this establishment on a plasticsupport without the presence of a feeder. The doubling time decreasesand then increases again, when the cells become rehabituated to this newenvironment.

EXAMPLE 5 Control of the Level of Serum for the Proliferation of theLines

During the obtaining of these lines, the culture media used areconventional culture media comprising a base (DMEM, GMEM, HamF12, McCoy,and the like) supplemented with various additives such as nonessentialamino acids, vitamins, and sodium pyruvate. This complex mediumcomprises fetal calf serum, which remains a central component of theculture, even though components of different origins, including plantcomponents, can be gradually used. A process for controlling andhabituating the cells to relatively low proportions of fetal calf serumis presented. It is thus possible to maintain cells in highproliferation (division time>1) with low percentages of serum (2% forexample in the case of the S86N16 cells).

The curves presented in FIG. 2 illustrates the relative reduction ofserum for a given cell type: S86N16 cells, The doubling time and themean division times were also calculated and presented in table 3. Itwill be noted that the mean division time increases as a function of therelative reduction in serum. A recovery phase is nevertheless observedafter some time in culture under the conditions mentioned. This timeremains nevertheless less than 24 h (d>1), which already represents avery advantageous proliferation in industrial terms even at serumconcentrations of 2%, which is already relatively low. Improvements withregard to the different metabolites to be used may be envisaged in orderto increase this time and still further optimize the culture conditions.

TABLE 3 Condition 10% 7.5% 3.75% 2% d 2.02 1.51 1.47 1.08 MDT 11.9 15.816.3 22.2

The examples are taken between passages p204 and p179 for the 10%condition, between p198 and p176 for the 7.5%, between p224 and p201 forthe 3.75% and between p216 and p199 for the 2%.

EXAMPLE 6 Deprivation of the Cells of Feeder Layer

Under the initial culture conditions, the presence of a layer ofinactivated cells appears to be necessary in order to obtain embryonicstem cells as was described above. This feeder layer no longer appearsto be necessary after a number of passages. Only the “culture treated”plastic appears to be important. Indeed, one of the characteristics ofsome eukaryotic cells is to proliferate in adherent form. In order tofacilitate the adhesion of the cells, the various plastic materials usedare “culture” treated. They undergo during their manufacture a treatmentwhich adds charges at the surface of the plastic, which charges promotethe adhesions of the extracellular matrix of the cells. By contrast, thecell culture untreated plastic, often called plastic of bacteriologicalquality, is not surface treated by addition of specific feeders. Theadhesion of the cells thereto is generally very difficult, or evenimpossible, or then induces changes in morphology, and in behavior whichare often drastic. This distinction between the two plastic qualitiesmakes it possible to obtain, depending on the inoculations which arecarried out therein, cells with different behaviors. Gradual deprivationof the cultures of inactivated “feeder” makes it possible to obtain,after a few passages, homogeneous cultures of stem cells directlyinoculated on “culture treated” plastic.

The comparative growth curves for the cells maintained in the presenceand in the absence of inactivated “feeder” are presented with the caseof the S86N16 cells in FIG. 3. This adaptation of the cells isprogressive so as not to lose the stem cell character of the cellsinitially maintained on a “feeder”. Progressive derivatives are thusmade. The obtaining of cells which proliferate on plastic is theaccomplishment of the withdrawal process. In table 4, the division timesshow sensitivity of the cells to their environment. As in the case ofthe progressive withdrawal of serum, an adaptation is obtained with arecovering effect on the cells after a few passages under the conditionsdefined.

TABLE 4 Condition 1.2 0.5 0.3 plastic d 1.95 1.84 1.39 1.42 MDT 12.3 1317.3 16.9

The examples are taken between the passages p154 and p131 for the 3conditions 1.2×10⁶, 0.5×10⁶ and 0.3×10⁶ feeder cells and between p161and p139 for the condition on plastic alone.

EXAMPLE 7 Deprivation of the Cells in Growth Factors

Under the initial culture conditions, the presence of growth factors isnecessary. It is possible to schematically distinguish two families offactors: the cytokines and the trophic factors.

The cytokines are mainly cytokines whose action is through a receptorwhich is associated with the gp130 protein. Thus, LIF, interleukin 11,interleukin 6, CNTF, oncostatin and cardiotrophin have a similar mode ofaction with the recruitment at the level of the receptor of a specificchain and the combination of the latter with the gp130 protein inmonomeric or sometimes heterodimeric form. In a few cases, thecombination of a soluble form of the receptors, a form described interalia for the receptors for interleukin 6 and CNTF, makes it possible toincrease the proliferative effect observed. It has been previously shownthat the addition of at least one of these cytokines appeared to benecessary for obtaining embryonic stem cells.

The trophic factors are mainly SCF, IGF-1 and bFGF, which are also usedat the start of the culture, as described above. Their presence is alsonecessary for obtaining and amplifying the cells.

By progressively reducing these growth factors, it is possible toobtain, after a few passages, culture conditions which allow theproliferation of the embryonic or somatic stem cells without theaddition of an exogenous growth factor. The different markers used tocharacterize these cells are always positive for the cells maintainedwith no factors.

EXAMPLE 8 Comparison of the Media Used

Inoculated into different media, the cells are not obtained with thesame frequencies. Comparison of the compositions of the media makes theidentification of one of the components in particular difficult. Itappears more likely that the whole combination allows an improvement inthe physiology of the cells. Among the preferred media, the Ham F12medium, the MacCoy medium, the DMEM medium and a DMEM medium enrichedwith biotin will be noted. Starting with such an isolate, adaptationtrials are carried out in these different media.

EXAMPLE 9 Establishment of the Nonadherent Cells

During the successive passages of the stem cells, a high-densityinoculation directly into the bacteriological dish makes it possible toobtain, after a few passages, embryonic cells which become detached fromtheir substrate and which proliferate in suspension in the form of smallregular aggregates. This proliferation is encouraged over severalpassages by mere dilution, mechanical dissociation and nonuse ofproteolytic enzyme. The stirring of the cultures is generally carriedout but does not represent a distinguishing factor for obtainingnonadherent cells. Like the adherent cells, these cells have acharacteristic morphology of stem cells, i.e. a small size, a largenucleocytoplasmic ratio, a nucleus with at least one nucleolus which isclearly visible and a very small cytoplasm. These cells arecharacterized by a growth in small aggregates which are more or lesscompact. These nonadherent cells exhibit cross-reactivity with a numberof antibodies, as described above in Pain et al., 1996. These cells arealso positive for the endogenous telomerase activity (as presented inexample 10 for the EB1, EB4 and EB5 cells). In a nonadherent phase, thecells exhibit a high proliferation in different media. The initialinoculation density and the very regular supply of fresh medium provideshigh densities which may range above 1×10⁶ cells per ml. Table 5summarizes the main characteristics of a few isolates (parental cells,initial passage of the making into a suspension, number of daysmaintained in culture in suspension, number of passages and ofgenerations obtained before voluntary stoppage of the maintenances). Itcan thus be noted that the passage for the making into a suspension canvary from one isolate to another (see isolate EB1 and EB14) and theproliferation rate (see isolate EB3 and EB14).

TABLE 5 Parental Initial Name cells passage Start Days PassagesGenerations EB1 S86N16 p111 20-01-2001 184 41 120 EB3 S86N16 p11823-01-2001 381 17 40 EB4 S86N45 p100 25-09-2001 44 17 40 EB5 S86N45 p10025-09-2001 44 17 40 EB14 S86N45 p81 05-09-2002 70 24 65

It will be noted that the term “start” corresponds to the cells beingplaced under nonadherence.

EXAMPLE 10 Characterization of the Established Cells

The stem cells maintained for long culture times are characterized withthe same criteria as those described above (Pain et al., 1996). It isthus possible to regularly detect the endogenous alkaline phosphataseactivity, illustrated by the photograph of FIG. 5, the endogenoustelomerase activity and reactivity with specific antibodies such as theantibodies SSEA-1 (TEC-01) and EMA-1.

One of the important criteria during the establishment of the cells isthe presence of telomerase. Various tests were carried out during themaintenance of the cells in culture using a TRAP detection kit(Telomerase PCR Elisa, Roche). The cells are detected positive aftervarious passages in culture. Thus, the telomerase activity is detectablefor the S86N16 cells, the S86N45 cells and for the EB1, EB4 and EB5cells which are derived therefrom in a nonadherent form (see table 6).The CEFs (Chicken Embryonic Fibroblasts) maintained in primary cultureare considered as negative. The threshold of an OD<0.2 is the thresholdrecommended by the kit as the negative threshold. All the analyses werecarried out on an equivalent of 2000 cells.

TABLE 6 Assay of the telomerase activity in various lines at variouspassages Cells Passage Telomerase OD S86N16 p12 1.7 p29 2.8 p185 0.97p204 0.95 S86N16 EB1 p134 1.1 S86N45 p50 0.87 p58 1.1 p66 0.96 p94 1.2S86N45 EB4 p112 1.4 S86N45 EB5 p112 0.94 CEF* p4 0.07

EXAMPLE 11 Transfection and Induction of the Cells

The stem cells maintained in a growth over the long term are transfectedwith various expression plasmids. It has been shown that avian stemcells could be transfected (Pain et al., 1996). In particular, thenonadherent cells are transfected and various sorting systems make itpossible to identify the stably transfected cells (cell sorting,limiting dilution, and the like). These genetic modifications can bemade at the undifferentiated stage of the stem cell. Once thismodification has been obtained, the cell is then induced todifferentiate spontaneously or by addition of a differentiation inducer.In this case, it is possible to use retinoic acid at concentrations of10⁻⁸ M to 10⁻⁶ M, or dimethyl sulfoxide at concentrations of 1 to 2%final or sodium butyrate at concentrations of 10⁻⁴ to 10⁻⁸ M, or phorbolester (TPA, PMA, and the like) or lipopolysaccharides (LPS) atconcentrations of 1 to 5 μg/ml final. In another example, the cells canform embryoid bodies in suspension, which embryoid bodies can be causedto adhere to plastic after dissociation or nondissociation of the cellsconstituting them. These differentiated cells then proliferate but havea more limited capacity for proliferation over the long term. Bytargeting the genetic modification on a gene which influences theproliferation of the cells, it is possible to make these differentiatedcells capable of proliferating over the long term.

EXAMPLE 12 Infection of the Cells

The adherent and nonadherent cells can be infected with differentviruses and retroviruses including avian viruses and retroviruses. Thesecells can thus serve as a replication support for the production ofviral stocks intended for the production of live, attenuated orinactivated human and veterinary vaccines depending on the cases. Amongthe viruses of interest, there may be mentioned those of the family ofadenoviruses (such as Human Adenovirus C, Fowl Adenovirus A, OvineAdenovirus D, Turkey Adenovirus B), circoviridae (such as Chicken AnemiaVirus, CAV), certain coronaviruses, such as avian infectious bronchitisvirus (IBV), flaviviruses (such as Yellow fever virus and hepatitis Cvirus), hepadnaviruses (such as Hepatitis B virus and Avihepadnavirusessuch as Duck hepatitis B virus); herpesviruses (such as Gallidherpesvirus, HSV (Herpes simplex virus) and Human herpesvirus 1, 3 and5), orthomyxoviruses (such as the influenza virus: Influenzavirus A,Influenzavirus B and Influenzavirus C), papovaviruses (such aspolyomavirus and more particularly Simian virus 40), paramyxoviruses(such as measles, mumps and rubella viruses and such as respirovirusesand pneumoviruses such as human respiratory syncytial virus andMetapneumovirus such as Avian pneumovirus), picornaviruses (such aspolio virus, hepatitis A virus, and such as Encephalomyocarditis virusand foot-and-mouth disease virus), poxviruses (such as fowlpox virus andavipox viruses including Canarypox viruses, Juncopox viruses, Mynahpoxviruses, Pigeonpox viruses, Psittacinepox viruses, Quailpox viruses,Sparrowpox viruses, Starlingpox viruses, Turkeypox viruses),orthopoxvirus such as vaccinia virus, MVA, and reoviruses (such asrotaviruses), retroviruses (such as ALV, avian leukosis virus,Gammaretroviruses such as Murine leukemia virus, Lentiviruses such asHuman immunodeficiency virus 1 and 2) and Togaviridae such as Rubivirus,in particular Rubella virus.

EXAMPLE 13 Protocol for Infecting a Nonadherent Avian Cell Line (EB1)with a Virus Amplification of the Cells:

The EB1 or EB14 cells are inoculated into a medium, preferably MacCoy's5A, HAMF12 or DMEM medium, or any other medium of interest, containing5% serum at a concentration of 0.2×10⁶ cells/ml for an initial volume of50 ml in general. They are maintained in culture at 39° C. and at 7.5%CO₂, with stirring. Fresh medium is added every day for the 3 to 4 daysfor which the amplification lasts in order to reach a cell concentrationof 1 to 3×10⁶ cells/ml for a final culture'volume of 100 to 250 ml.

The cells in suspension are collected and centrifuged for 10 min at 1000 rpm approximately. The pellet is resuspended in 20 to 50 ml of 1×PBS(Phosphate buffer Salt). The cells are then counted, centrifuged and thepelleted cells are taken up in a serum-free medium at a finalconcentration of 3 to 5×10⁶ cells/ml. Several tubes are then preparedunder these conditions containing 3 to 5×10⁶ cells per tube.

Preparation of the Virus and Infection:

The viral stock having a known titer is rapidly thawed at 37° C. anddiluted in serum-free medium at a titer of 10× to 1 000× theconcentration necessary for the final infection. The cells are infectedwith the virus of interest at an m.o.i. (multiplicity of infection) of0.01 to 0.5 according to the types of virus, which involves addingbetween 0.1 and 10% volume/volume of viral suspension to the cellularpellet. After incubating for 1 hour at an optimum temperature for thevirus, in general from 33 to 37° C., the cells are again centrifuged andthe medium removed with care. This step is found to be often necessaryin order to limit the effect of the initial virus in the subsequentprocess. One of the possibilities is to directly dilute the cellswithout centrifuging them again with serum-containing medium (5% ofserum) at a final concentration of 0.2 to 1×10⁶ cells/ml and incubatedagain.

Harvesting of the Supernatant and of the Cells:

After 2 to 4 days of incubation, depending on the viral kinetics and thepotential cytopathic effect of certain viruses, the medium containingthe cells or the cellular debris is harvested. Depending on the viruses,only the pellet or the supernatant may be of interest and contain theviral particles. The cells are harvested and centrifuged. The collectedsupernatant is centrifuged again for 5 to 10 minutes at 2 500 rpm, andstored at −80° C. before purification of the particles.

An aliquot is collected in order to carry out the titration. Thecellular pellet is taken up in 5 ml of serum-free medium, sonicated andcentrifuged for 5 to 10 minutes at 2 500 rpm. The supernatant obtainedis stored at −80° C. up to the purification and the titration of analiquot.

The viral infection and production efficiencies are compared between thevarious conditions performed.

For the viruses with cytopathic effects, the titrations are in generalcarried out by the lysis plaque technique.

EXAMPLE 14 Protocol for Infecting an Adherent Avian Cell Line (S86N45)with a Virus Preparation of the Cells:

The cells are inoculated 48 hours before the infection into T150 flasksat a concentration of between 0.03 and 0.06×10⁶ cells/cm² in a medium,preferably MacCoy's 5A, HAMF12 or DMEM medium, or any other medium ofinterest, containing 5% serum. They are maintained at 39° C. and 7.5%CO₂.

Infection:

The viral stock having a known titer is rapidly thawed at 37° C. anddiluted in serum-free medium at a titer of 10× to 1 000× theconcentration necessary for the final infection. The cells are infectedwith the virus of interest at an m.o.i. (multiplicity of infection) of0.01 to 0.5 according to the types of virus, which involves addingbetween 0.1 and 10% volume/volume of viral suspension to the cellularpellet. The infection is generally carried out in a minimum of medium(from 5 to 10 ml for a 75 cm² flask) in a medium containing 0% serum.

After incubating for 1 hour at the optimum temperature for the virus, ingeneral from 33 to 37° C., 20 ml of medium 5% are added to the flasks.In a particular case, the cells can be washed with PBS in order toremove the particles which might be attached to the cells. In the caseof a cytopathic virus, the cells are observed daily after the infectionin order to monitor the appearance of the cell lysis plaque, whichindicates good progress of the infection.

Harvesting of the Supernatant and of the Cells:

After 2 to 4 days of incubation, depending on the viral kinetics and thepotential cytopathic effect of certain viruses, the medium containingthe supernatant, the cells and the cellular debris are harvested.Depending on the viruses, only the pellet or the supernatant may be ofinterest and contain the viral particles. The cells are harvested andcentrifuged. The collected supernatant is centrifuged again for 5 to 10minutes at 2 500 rpm, and stored at −80° C. before purification of theparticles. An aliquot is collected in order to carry out the titration.The cellular pellet is taken up in 5 ml of serum-free medium, sonicatedand centrifuged for 5 to 10 minutes at 2 500 rpm. The supernatantobtained is stored at −80° C. up to the purification and the titrationof an aliquot.

The viral infection and production efficiencies are compared between thevarious conditions performed.

For the viruses with cytopathic effect, the titrations are in generalcarried out by the lysis plaque technique.

EXAMPLE 15 Replication of a Recombinant Avipox on Nonadherent Avian StemCells of the EB1 Line

The nonadherent stem cells EB1 at passage 138 are amplified and theninfected at an m.o.i. of 0.1 with a recombinant avipox producing aprotein of interest.

After the infection, the cells are maintained in a spinner for the 4days for which the infection lasts. An aliquot is removed from thesecond day and then the net two days in order to monitor the variationof the viral titer both in the supernatant and in the intracellularcontent, after lysis of the cellular content. The titration is carriedout by the lysis plaque technique.

Table 7 illustrates the results obtained. These results demonstrate thevery satisfactory replication of the recombinant avipox on the EB1 stemcells. Thus, the infectious titer progresses throughout the culture andthe course of the infection, reaching a maximum of 7.2 PFU/cell (PFU:Plating Forming Unit) after 4 days of incubation. This titer is at leastequivalent to that obtained for this same recombinant avipox on primarychicken embryo cells.

This titer can be improved by specific culture conditions andoptimization procedures.

It will also be noted that at least equivalent infectious titers werealso obtained on a larger scale in 3 liter bioreactors.

TABLE 7 Kinetics of titration of the recombinant avipox on nonadherentEB1 stem cells Sampling (h after infection) 50 hours 74 hours 97 hoursCellular fraction 6.40 6.37 5.99 (Log PFU/ml) Supernatant 5.56 5.8 6.29(Log PFU/ml) Total 5.78 5.94 6.31 (Log PFU/ml) PFU/cell 2.2 3.2 7.2

EXAMPLE 16 Replication of Modified Vaccinia Virus Ankara (MVA) onAdherent and Nonadherent Avian Stem Cells of the S86N45 Line and EB14Line

The MVA virus (titer 2.5×107 TCID50/ml in 0.5 ml vials) was receivedunder frozen conditions.

For safety reasons, the MVA virus and infected cells were kept undercontrolled conditions (−80° C. freezer) and the contaminated plasticmaterial was placed into hypochloride solution for more than 1 hour andthen place into a bag for full and complete autoclave inactivation.

Experiments and Results

The S86N45 and EB14 cells were thawed in a HamF12 based complete medium.

The adherent S86N45 cells were amplified quite rapidly, with a goodgrowth rate and a nice morphology.

The cells were infected 1 hour in 2 ml of PBS with the different m.o.i.of interest with no washing with PBS after the infection. The medium wasjust added to the complete infectious medium, i.e. the added virus wasnot removed.

After 3 days of infection, the cell lysis appears to be proportional tothe used m.o.i. This cytopathic effect is a good indicator of the virusinfection of the cells. So cells and supernatant are harvested andstored at −80° C. before purification of particles and/or titration.

The non adherent EB14 cells were amplified. The cells were infected, notwashed, and the complete medium directly added on the inoculum after 1hour of contact with viral particles. After 3 days, a characteristiccell lysis was observed. The non infected cells used as the control werecounted and a good growth was demonstrated, showing good cultureconditions and therefore confirming an efficient lysis by the virus inthe infected culture. Cells and supernatant are harvested and stored at−80° C. before purification of particles and/or titration (see table 8).

TABLE 8 Results of the titration Titer/mL Average Virus/ based on Virusvirus pellet of 14 ml total yield/ yield/ Cell Type M.O.I. Trial 10E6cells volume cell cell S86N45 0 1 0 0 0 0 0 2 0 0 0 0.1 1 1-3 ×10{circumflex over ( )}7 ≧6 × 10{circumflex over ( )}5  5-15  5-15 0.1 21-3 × 10{circumflex over ( )}6 1-3 × 10{circumflex over ( )}5 1-5 0.01 11-3 × 10{circumflex over ( )}7 1-3 × 10{circumflex over ( )}6 15-30 ≧300.01 2 4-6 × 10{circumflex over ( )}7 1-3 × 10{circumflex over ( )}6 ≧30EB14 0 1 0 0 0 0 0.1 1 1-3 × 10{circumflex over ( )}7 1-3 ×10{circumflex over ( )}6 15-30 15-30 0.1 2 1-3 × 10{circumflex over( )}7 1-3 × 10{circumflex over ( )}6 15-30 0.05 1 ≧6 × 10{circumflexover ( )}7 4-6 × 10{circumflex over ( )}6 ≧50 ≧50 0.05 2 1-3 ×10{circumflex over ( )}7 1-3 × 10{circumflex over ( )}6 15-30 0.01 1 1-3× 10{circumflex over ( )}7 1-3 × 10{circumflex over ( )}6 15-30 15-300.01 2 1-3 × 10{circumflex over ( )}7 1-3 × 10{circumflex over ( )}615-30

Applicants hereby incorporate by reference PCT/FR03/00735 filed on Mar.7, 2003, and French application serial no. 0202945 filed Mar. 8, 2002,and all references cited herein.

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1. An avian cell line obtained from embryonic stem cells of fertilizedeggs characterized by a status of proliferation and non differentiationwherein said cell line is capable of proliferating in a basal culturemedium free of exogenous growth factors and cytokines, serum, and/orfeeder layer for at least 50 days and wherein said cell line has atleast one of the following features: a very visible nucleola and verysmall nucleoplasm, an endogenous alkaline phosphatase activity, anendogenous telomerase activity, and reactivity with specific antibodiesselected from the group of antibodies SSEA-1 (TEC01), SSEA-3 and EMA-1.2. The avian cell line according to claim 1, wherein said embryonic stemcells originate from blastodermal disks of fertilized eggs.
 3. The aviancell line according to claim 1, wherein said embryonic stem cells arechicken embryonic stem cells.
 4. The avian cell line according to claim1, wherein said cell line has been obtained by a method comprising thefollowing steps: a) culturing embryonic stem cells obtained fromblastodermal disks of fertilized eggs in a culture medium comprising: atleast a growth factor selected from the group of SCF, IGF-1 and bFGF andat least one cytokine selected from LIF, IL-11, IL-6, IL-6R, CNTF,oncostatin and cardiotrophin; an inactivated feeder layer of STO cells;and fetal calf serum at a concentration of 12 to 8%, b) after abouttwenty passages, modifying the culture medium: by gradual withdrawal ofsaid growth factors and cytokines; or by gradual withdrawal of thefeeder layer; or by decreasing the fetal calf serum concentration toreach a low concentration of 2%, tending toward 0% (serum-free medium),and c) establishing adherent or non-adherent cell lines capable ofproliferating in a basic medium in the absence of exogenous growthfactors and cytokines, serum or the inactivated feeder layer.
 5. Theavian cell line according to claim 4, wherein the cell culture medium ofstep a) contains at least one cytokine, bFGF, and SCF.
 6. The avian cellline according to claim 4, wherein the cell culture medium of step a)contains at least the growth factors and cytokines consisting of SCF,IGF-1, CNTF, IL-6, soluble IL-6R, and bFGF.
 7. The avian cell lineaccording to claim 6, wherein that the cell culture medium of step a)further contains IL-11.
 8. The avian cell line according to claim 4,wherein the culture medium modification of step b) comprises gradualwithdrawal of said growth factors and cytokines followed by progressivedeprivation of said feeder layer of STO cells and/or the decreasing ofthe concentration of fetal calf serum to reach a low concentration of2%, tending toward 0% (serum-free medium).
 9. The avian cell lineaccording to claim 1, wherein said cell line is an adherent cell line.10. The avian cell line according to claim 1, wherein said cell line isa non-adherent cell line.
 11. The avian cell line according to claim 10,wherein said non-adherent cell line has been obtained by inoculating thecells obtained in step c) at high-density into a bacteriological dishfollowed by several passages in mere dilution.
 12. The avian cell lineaccording to claim 11, wherein the initial inoculation density is of atleast 1×10⁶ cells/mL.
 13. The avian cell line according to claim 1,characterized by a status of proliferation and non differentiation andwherein said cell line has the following features: a very visiblenucleola and very small nucleoplasm, an endogenous alkaline phosphataseactivity, an endogenous telomerase activity, and reactivity withspecific antibodies selected from the group of antibodies SSEA-1(TEC01), SSEA-3 and EMA-1.
 14. The avian cell line according to claim13, wherein said cell line presents reactivity with an antibody selectedfrom the group consisting of antibodies SSEA-1 (TEC01) and EMA-1. 15.The avian cell line according to claim 1, wherein said cell line iscapable of proliferating for at least 100 days.
 16. The avian cell lineaccording to claim 1, wherein said cell line is capable of proliferatingfor at least 150 days.
 17. The avian cell line according to claim 1,wherein said cell line is capable of proliferating for at least 300days.
 18. The avian cell line according to claim 1, wherein said cellline is capable of proliferating for at least 600 days.
 19. The aviancell line according to claim 1, wherein said basal culture medium isselected from the group of medium consisting of DMEM, GMEM, HamF12, andMcCoy's 5A supplemented with additives.
 20. The avian cell lineaccording to claim 19, wherein said additives are chosen fromnon-essential amino acids, vitamins, and sodium pyruvate.